1. Field of the Invention
The present invention relates to a process for producing an unsaturated alcohol, in which an unsaturated aldehyde is hydrogenated to give a corresponding unsaturated alcohol in the presence of a novel catalyst. In particular, the present invention relates to a process for producing an .alpha., .beta.-unsaturated alcohol, in which an unsaturated aidehyde is used as a starting material, and only the aidehyde group in the unsaturated aidehyde is selectively hydrogenated by hydrogen transfer reaction from an alcohol in the presence of a catalyst containing the specific metallic oxide as an active ingredient, while leaving the carbon-carbon double bond as it is, to give the corresponding .alpha., .beta.-unsaturated alcohol.
2. Description of the Prior Art
An unsaturated aidehyde has both a carbon-carbon double bond and a carbonyl group as functional groups in the same molecule. However, it is extremely difficult to selectively reduce only one of the functional groups. In particular, in the case of an .alpha., .beta.-unsaturated carbonyl compound in which a double bond and a carbonyl group have a conjugated relationship with each other, an alkenyl group hydrogenates more easier than the carbonyl group. Therefore, in such case, the by-products of hydrogenation, such as saturated aldehydes and saturated alcohols, or other various by-products of condensation reaction are produced, resulting in the greater difficulty in selective hydrogenation.
Various methods have been attempted to selectively hydrogenate the aldehyde group in .alpha., .beta.-unsaturated aldehydes, such as acrolein, while leaving the unsaturated bond as it is, and to produce the corresponding .alpha., .beta.-unsaturated alcohol in high yields.
Numerous direct hydrogenating methods have been proposed. For example, there is the long-standing method using noble metals of the platinum group as catalysts (W. F. Tuley, R. Adams, J. Am. Chem. Soc., 47, 3061 (1925)); methods using catalysts mainly composed of copper-cadmium (U.S. Pat. No. 2,763,696), silver-zinc (Japanese Patent Laid-open No. 47-13010) or silver-cadmium (Japanese Patent Laid-open No. 53-18506) as catalysts able to give relatively high yield; and improved methods thereof (Japanese Patent Laid-open Nos. 64-159054 and 64-1207041).
However, the catalysts used in these methods do not exhibit enough high selectivity for the hydrogenating reaction. In addition, many of such catalysts contain harmful compounds. Therefore, from a safety point of view, they have not been used in large amounts industrially.
On the other hand, methods taking the place of those above have also been attempted, in which unsaturated alcohols are synthesized by utilizing the hydrogen transfer reaction from alcohol as a hydrogen source.
For example, there have been proposed methods using catalysts, such as catalysts containing alkali metals and alkaline earth metals, e.g., magnesium oxide, calcium oxide and lithium oxide, as active ingredients (S. A. Ballard et. al, "Advances in Catalysis" Vol. IX, Academic Press, (1957)); and catalysts represented by the general formula: EQU MgaXbYcOd
(in which X represents boron, aluminum, silicon, yttrium, niobium, lanthanum, etc., Y represents an alkali metal and/or an alkaline earth metal other than magnesium, O represents oxygen, and a, b, c and d are atomic ratios of Mg, X, Y and O, respectively) (Japanese Patent Laid-open No. 62-30552).
In addition, other silver-based catalysts used in direct hydrogenation have also been proposed (Japanese Patent Publication No. 51-42042).
However, the catalysts used in above methods exhibit low activity and selectivity, and the activity changes with the passage of time. Therefore, it is difficult to say that such catalysts have reached to an industrial level of use.